1. Field of Invention
The invention relates to a display panel and a display device having the display panel.
2. Related Art
With the progress of technologies, flat display devices have been widely applied to various kinds of fields. Especially, liquid crystal display (LCD) devices, having advantages such as compact structure, low power consumption, less weight and less radiation, gradually take the place of cathode ray tube (CRT) display devices, and are widely applied to various electronic products, such as mobile phones, portable multimedia devices, notebooks, LCD TVs and LCD screens.
A conventional LCD device includes a thin film transistor (TFT) substrate, and the TFT substrate includes a TFT and a pixel electrode which are both disposed on a substrate. In the manufacturing process, a via needs to be formed by etching the portion over the drain of the TFT and a transparent conductive layer is disposed on the inner wall of the via to electrically connect the drain of the TFT and the pixel electrode. Besides, the gate of the TFT is electrically connected with a scan line and the source of the TFT is electrically connected with a data line. When the scan line inputs a scan signal to the gate of the TFT, the TFT is controlled so that the data voltage of the data line can be inputted to the pixel electrode through the source, the drain and the transparent conductive layer, and thereby the orientation of the liquid crystal can be controlled for the image display.
Moreover, the conventional polycrystalline TFT has a carrier mobility of about 100 cm2/Vs. However, it needs to be made under the environment of over 450° C., so it only can be formed on the substrate with high heat resistance and is not suitable for the application of large-size or flexible substrate. Besides, although the conventional amorphous TFT can be formed under the environment of lower temperature, e.g. about 300° C., this kind of amorphous TFT only has carrier mobility of about 1 cm2/Vs, so it can't be applied to the panel requiring high fineness. Therefore, it has been presented that the metal oxide semiconductor, such as indium gallium zinc oxide (IGZO), can be used as the channel layer of the TFT.
Although IGZO TFT has more excellent carrier mobility than the amorphous TFT and the process thereof is easier than the process of the polycrystalline TFT, IGZO TFT is very sensitive to the light, water and oxygen.
For protecting the channel layer of the TFT, a protection layer (such as silicon oxide) is disposed on the channel layer of metal oxide semiconductor to protect the channel layer in the conventional art. FIG. 1A is a schematic diagram showing the electric characteristic curve of the TFT when a protection layer is disposed on the channel layer of metal oxide semiconductor. Although the protection layer has been disposed to protect the channel layer, after a period of time (or after a heat treatment), as shown in FIG. 1B, the characteristic curve of the TFT still deviates from the curve in FIG. 1A. Therefore, the efficiency of the TFT will be reduced and the display quality of the display panel and display device will be thus affected.
Therefore, it is an important subject to provide a display panel and a display device which include stable TFT efficiency so as to have a stable display quality.